1. Field
The present invention relates to a pixel and an organic light emitting display device using the same.
2. Description of Related Art
Recently, various flat panel displays (FPDs) having reduced weight and volume to address disadvantages of cathode ray tubes (CRTs) have been developed. The FPDs include liquid crystal display devices (LCDs), field emission display devices (FEDs), plasma display panels (PDPs), organic light emitting display devices, and the like.
Among the FPDs, the organic light emitting display devices display images using organic light emitting diodes (OLEDs) that emit light through the recombination of electrons and holes. The organic light emitting display devices have fast response speed and are driven with low power consumption.
FIG. 1 is a circuit diagram illustrating a related art pixel of a conventional organic light emitting display device. Referring to FIG. 1, a pixel 4 of the organic light emitting display device includes an OLED and a pixel circuit 2 coupled to a data line Dm and a scan line Sn to control the OLED.
An anode electrode of the OLED is coupled to the pixel circuit 2, and a cathode electrode of the OLED is coupled to a second power source ELVSS. The OLED is configured to generate light with a luminance corresponding to a current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the OLED in accordance with a data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn. The pixel circuit 2 includes a second transistor M2″ coupled between a first power source ELVDD and the OLED, a first transistor M1″ coupled between a gate electrode of the second transistor M2″ and the data line Dm, and a storage capacitor Cst″ coupled between the gate electrode of the second transistor M2″ and a first electrode of the second transistor M2″.
A gate electrode of the first transistor M1″ is coupled to the scan line Sn, and a first electrode of the first transistor M1″ is coupled to the data line Dm. A second electrode of the first transistor M1″ is coupled to a first terminal of the storage capacitor Cst″. Here, the first electrode is a source electrode or a drain electrode, and the second electrode is the other one of the source and drain electrodes. For example, when the first electrode is the source electrode, the second electrode is the drain electrode, and vice versa. When a scan signal is supplied from the scan line Sn, the first transistor M1″ is turned on in order to supply a data signal from the data line Dm to the storage capacitor Cst″. At this time, a voltage corresponding to the data signal is charged in the storage capacitor Cst″.
The gate electrode of the second transistor M2″ is coupled to the first terminal of the storage capacitor Cst″, and the first electrode of the second transistor M2″ is coupled to both a second terminal of the storage capacitor Cst″ and the first power source ELVDD. A second electrode of the second transistor M2″ is coupled to an anode electrode of the OLED. The second transistor M2″ controls an amount of current that flows from the first power source ELVDD to a second power source ELVSS via the OLED in accordance with the voltage stored in the storage capacitor Cst″. At this time, the OLED emits the light corresponding to the amount of current supplied from the second transistor M2″.
In an organic light emitting display device, threshold voltages of driving transistors (e.g., M2″ in FIG. 1) included in respective pixels may be different from one another due to process variations and the like. When the threshold voltages of the driving transistors are different from one another, lights of different luminance are produced even though a data signal corresponding to the same gray level is supplied to each of the respective pixels. Therefore, research on ways to achieve more uniform luminescence is ongoing.